As a technique for capturing a clear image in focus, an autofocus technique has been known in which the focus is automatically adjusted to a prescribed position. As schemes of the autofocus techniques, a phase difference scheme, a contrast scheme, and so forth have been known. In recent years, an autofocus of the contrast scheme is installed in many compact digital cameras and cameras installed in smart phones. Those techniques cause an object in focus to be recorded clearly and an object out of the range of the depth of field to be recorded in a blurry condition in one image as a photographed image.
Meanwhile, in recent years, high-speed consecutive photographing has become possible, and a technique has been developed that composes an image with an increased depth of field from plural consecutively photographed images. Such a technique enables acquisition of an image in which objects in a wide range from a close view to a distant view are simultaneously focused.
However, due to the increase in the depth of field, gradation saturation in a partial area in an image, which has not been a problem in related art, is recognized as degradation of image quality. For example, in a case where a person in a close view is photographed and where the gradation is saturated due to a too bright distant view, an object that would be photographed in focus becomes an image similar to a blurry object in related art.
Thus, a technique has been suggested that is capable of increasing the depth of field and the dynamic range, and one example is PTL 1. One embodiment of PTL 1 discloses a method in which photographing is performed by adjusting the focus for each sensitivity of an image capturing apparatus and composition from plural photographed images is thereby performed. However, in this method, degradation of image quality occurs around the object that is photographed out of the depth of field. PTL 1 discloses this fact. Thus, another embodiment of PTL 1 discloses that photographing is performed for each of photographing sensitivities while the focus is changed and composition from plural images is thereby performed. That is, the dynamic range is increased by images at different sensitivities in which the depth of field is increased, or the depth of field is increased by images in different focuses in which the dynamic range is increased, and increases in the depth of field and the dynamic range are thereby realized.